在 Automapper 中展平自引用对象

Question

我有一个自引用模型，我想将其转换为平面列表。模型如下所示。

public class Node
{
    public List<Node> Nodes { get; set; }

    public Person Person { get; set; }

    public Language Language { get; set; }
}

public class NodeDTO
{
    public PersonDTO Person { get; set; }

    public LanguageDTO Language { get; set; }
}

public class NodeListDTO
{
    public List<NodeDTO> Nodes { get; set; }
}

我希望层次结构中的所有节点都被展平为我的 DTO 对象中的一个列表。 Auto Mapper 可以做到吗？

我尝试使用自定义值解析器，但我还没有弄清楚如何在值解析器中使用 PersonDTO 和 LanguageDTO 的映射。

Answer 1

首先，您需要代码来扁平化节点层次结构。 AutoMapper 不会自动执行此操作。我为此使用了以下扩展方法：

public static IEnumerable<T> Flatten<T>(this T root,
   Func<T, IEnumerable<T>> childrenSelector)
{
    if (!typeof(T).IsValueType && root == null)
        throw new ArgumentNullException(nameof(root));

    return Flatten(new[] { root }, childrenSelector);
}

public static IEnumerable<T> Flatten<T>(this IEnumerable<T> source,
    Func<T, IEnumerable<T>> childrenSelector)
{
    if (source == null)
        throw new ArgumentNullException(nameof(source));

    if (childrenSelector == null)
        throw new ArgumentNullException(nameof(childrenSelector));

    return FlattenIterator(source, childrenSelector);
}

private static IEnumerable<T> FlattenIterator<T>(this IEnumerable<T> source,
    Func<T, IEnumerable<T>> childrenSelector)
{
    if (source != null)
    {
        foreach (var item in source)
        {
            yield return item;
            var children = childrenSelector(item);
            if (children != null)
                foreach (var child in FlattenIterator(children, childrenSelector))
                    yield return child;
        }
    }
}

接下来 - 您需要告诉 AutoMapper 如何展平节点层次并将其映射到列表

MapperConfiguration config = new MapperConfiguration(c =>
{
    c.CreateMap<Person, PersonDTO>();
    c.CreateMap<Language, LanguageDTO>();
    c.CreateMap<Node, NodeDTO>();
    c.CreateMap<Node, NodeListDTO>()
        .ForMember(d => d.Nodes, o => o.ResolveUsing(s => s.Flatten(n => n.Nodes)));
});

现在你可以简单地使用

var node = new Node {
    Person = new Person { Id = 1, Name = "Bob" },
    Language = new Language { Id = 10, Code = "en" },
    Nodes = new List<Node> {
            new Node {
            Person = new Person {  Id = 3, Name = "Mike"},
            Language = new Language {  Id = 11, Code = "es"},
            Nodes = new List<Node> {
                    new Node {
                    Person = new Person {  Id = 4, Name = "Alex"},
                    Language = new Language {  Id = 11, Code = "es"}
                }
            }
        },
        new Node {
            Person = new Person {  Id = 5, Name = "Serge"},
            Language = new Language {  Id = 12, Code = "by"}
        }
    }
};

var nodeListDTO = mapper.Map<NodeListDTO>(node);

结果：

{
  "Nodes": [
    {
      "Person": { "Id": 1, "Name": "Bob" },
      "Language": { "Id": 10, "Code": "en" }
    },
    {
      "Person": { "Id": 3, "Name": "Mike" },
      "Language": { "Id": 11, "Code": "es" }
    },
    {
      "Person": { "Id": 4, "Name": "Alex" },
      "Language": { "Id": 11, "Code": "es" }
    },
    {
      "Person": { "Id": 5, "Name": "Serge" },
      "Language": { "Id": 12, "Code": "by" }
    }
  ]
}